Sauna and Endurance Performance: The Science
Key insights
- Post-exercise sauna use is a practical form of heat acclimation. Its main endurance-relevant effect is expanding blood plasma volume, which improves cardiovascular efficiency.
- In the key runners study, three weeks of post-exercise sauna raised run time to exhaustion by 32%, alongside a 7.1% rise in plasma volume — though the sample was only six athletes.
- Plasma volume can expand meaningfully after roughly four post-exercise sauna sessions in trained cyclists, so early adaptations arrive fast.
- Heat adaptation shows cross-adaptation: sauna and hot-water immersion improve endurance in the heat, and may modestly help in temperate conditions too.
- A sensible protocol is roughly 20–30 minutes of sauna immediately after training, three to four times a week, with careful rehydration.
Runners and cyclists increasingly ask whether the sauna is more than a pleasant way to unwind after a hard session. The question is a fair one: heat exposure places a genuine physiological load on the body, and the adaptations it provokes overlap with several that endurance athletes actively chase. Chief among them is an expansion of blood plasma volume, the watery component of blood that governs how efficiently the cardiovascular system can deliver oxygen and shed heat.
The short answer is that post-exercise sauna bathing can improve endurance, chiefly by driving heat acclimation and the plasma-volume expansion that comes with it. The effect is best evidenced for performance in hot conditions, with more modest and less certain benefits in cool weather. As with most training tools, the magnitude is real but not miraculous, and the quality of the underlying evidence deserves an honest look.
This article walks through the plasma-volume mechanism, the landmark study in competitive runners, the broader heat-acclimation literature, and a practical protocol for folding sauna sessions into an endurance training week.
The Plasma-Volume Mechanism
When you sit in a sauna, your core temperature rises and your body works hard to shed heat: skin blood flow increases and you sweat. Repeated over days and weeks, this thermal load prompts the body to hold on to more fluid in the bloodstream, expanding plasma volume. A larger plasma volume increases the total volume of blood the heart can move with each beat, which lowers heart rate at a given workload, improves the delivery of oxygen to working muscle, and supports better sweating and cooling. Périard, Racinais and Sawka, in their review of the mechanisms of human heat acclimation, describe plasma-volume expansion as one of the earliest and most consistent adaptations to repeated heat exposure, contributing to reduced cardiovascular and thermal strain during subsequent exercise 4.
Crucially, these adaptations arrive quickly. In a study of seven well-trained cyclists who added roughly 30 minutes of sauna at about 87°C immediately after normal training, plasma volume was already meaningfully expanded after only four sessions 2. That rapid response is what makes post-exercise sauna a practical tool: an athlete does not need to relocate to a hot climate to gain a hallmark of heat acclimation.
The Runners Study And The Heat-Acclimation Data
The most frequently cited work on this topic is Scoon and colleagues' 2007 study of competitive male distance runners. In a cross-over design, six runners completed three weeks of post-training sauna bathing (around 30 minutes at roughly 90°C after each session) and, separately, three weeks of normal training. Relative to control, sauna bathing increased run time to exhaustion by 32%, an improvement the authors estimated to be worth about 1.9% in an endurance time-trial 1. Plasma volume rose by 7.1% and red-cell volume by 3.5%, consistent with the mechanism described above.
That 32% figure is eye-catching, but it should be read with care. The sample was only six athletes, run time to exhaustion is a sensitive test that tends to amplify percentage changes, and the more meaningful time-trial estimate of roughly 1.9% is a better guide to real-world impact. It is a genuine and worthwhile improvement for a competitive runner, not the dramatic leap the headline number implies.
The wider heat-acclimation literature supports and contextualises these findings. Post-exercise hot-water immersion — a close cousin of sauna use — has been shown to induce heat acclimation and improve endurance performance in the heat, lowering resting and exercising core temperature over a six-day protocol 3. And the review by Périard and colleagues concludes that heat acclimation reliably improves aerobic performance in warm and hot environments, with the possibility of smaller benefits in temperate conditions 4. The strongest, most consistent gains therefore appear when you later compete in the heat; the case for cool-weather benefit is real but more modest.
Realistic Expectations And Who Benefits
So, is sauna good for runners and cyclists? For endurance athletes preparing for a hot race — a summer marathon, a warm-weather triathlon, a stage race in the heat — the answer is a confident yes. Heat acclimation via sauna offers a well-supported route to the plasma-volume expansion and thermoregulatory adaptations that protect performance when the mercury climbs, without needing to travel to a hot climate.
For athletes racing exclusively in cool conditions, the picture is more nuanced. Some cross-adaptation to temperate performance is plausible and is hinted at in the evidence, but it is smaller and less certain than the benefit in the heat. Sauna use is best viewed as a complement to structured training rather than a substitute for it. It will not replace intervals, long runs or sensible progression — but for the right athlete at the right time, it is a low-cost, well-tolerated addition.
A Practical Post-Exercise Sauna Protocol
The studies converge on a broadly similar approach. Use the sauna immediately, or very soon, after a training session, when the body is already warm and primed to adapt. Aim for roughly 20–30 minutes per session at a traditional sauna temperature, building tolerance gradually rather than forcing a long first session. Three to four sessions per week over two to three weeks is enough to drive meaningful plasma-volume expansion, and the first adaptations can appear within the opening week.
Hydration is non-negotiable. Sauna sessions add to the sweat losses of training, so rehydrate deliberately afterwards with fluid and electrolytes, and skip the sauna if a session has left you already depleted or unwell. Because heat is an additional stressor, it is wise to schedule sauna blocks in a build phase rather than a heavy taper, and to reduce frequency if sleep or recovery start to suffer. For context on how sauna fits alongside other recovery goals, see our guide to using the sauna after a workout.
The Contrast Market Perspective
At Contrast Market, we see heat acclimation as one of the most evidence-backed reasons for an endurance athlete to own a quality sauna: the plasma-volume adaptation is real, arrives quickly, and pays off most when it matters, on a hot race day. If you would like help matching a sauna to your training goals and space, Schedule a consultation with our team.
References
The claims above draw on peer-reviewed research in exercise physiology, including the Scoon runners study, sauna- and immersion-based heat-acclimation trials, and a major review of heat-acclimation mechanisms. Full citations with PubMed links are listed in the footnotes below.
Footnotes
- Scoon GS, Hopkins WG, Mayhew S, Cotter JD (2007). Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. Journal of Science and Medicine in Sport. PubMed ↩︎
- Stanley J, Halliday A, D'Auria S, Buchheit M, Leicht AS (2015). Effect of sauna-based heat acclimation on plasma volume and heart rate variability. European Journal of Applied Physiology. PubMed ↩︎
- Zurawlew MJ, Walsh NP, Fortes MB, Potter C (2016). Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. Scandinavian Journal of Medicine & Science in Sports. PubMed ↩︎
- Périard JD, Racinais S, Sawka MN (2015). Adaptations and mechanisms of human heat acclimation: applications for competitive athletes and sports. Scandinavian Journal of Medicine & Science in Sports. PubMed ↩︎